The present invention relates generally to door holders of the type employing an electromagnet to maintain a door such as a fire door in an open position and more particularly to an electromagnetic flux generator and power control circuit for such a door holder.
Door holders which incorporate an electromagnet are well known as shown in several U.S. Patents. The door holder is typically employed with an armature assembly which is mounted to a door and is also well known in the art.
Generally, electromagnetic door holders are designed to be supplied electric power at 12, 24 or 120 volts. Some units are designed for operation with alternating current while other units rely on a supply of direct current. Some magnetic door holders are known which will work on either alternating or direct current by incorporating some sort of rectifier circuit.
In use, door holders typically operate in an essentially continuous fashion for maintaining fire doors and the like in an open position. In the event of a fire or other emergency, power supplied to the door holder is removed thus allowing the door to close under influence of a biasing force. Since the door holder in normal conditions is continuously operative, it is desirable to minimize the power requirement of the door holder to conserve electric power and the related costs.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.